The present disclosure relates generally to methods and apparatus for ranging techniques to determine distance and direction between nearby conductors.
With much of the world's easily obtainable oil having already been produced, new techniques are being developed to extract less accessible hydrocarbons. These techniques often involve drilling a borehole in close proximity to one or more existing wells. Examples of directed drilling near an existing well include intersection for blowout control, multiple wells drilled from an offshore platform, and closely spaced wells for geothermal energy recovery. Another such technique is steam-assisted gravity drainage (SAGD) that uses a pair of vertically-spaced, horizontal wells less than 10 meters apart. Careful control of the spacing is important to the technique's effectiveness.
One way to direct a borehole in close proximity to an existing well is “access-dependent active ranging” in which an electromagnetic source is located in the existing well and monitored via sensors on the drill string. Systems that locate both the source and the sensors on the drill string are often termed “access-independent active ranging”. Existing ranging techniques often only consider one surrounding casing of an existing well (e.g., a target well) relative to the drilling well, and are unable to identify multiple targets downhole, which limits the use of these techniques.